The pencil-billed shorebirds able to stay in the air for a week – flying from Alaska to New Zealand – rely on a few mudflat crescents to fuel this incredible journey.
Scientists recently found that almost the entire population of Band-tailed Godwits that breed in Alaska feed on clams and worms on ephemeral sandbanks just west of the mouth of the Kuskokwim River. In the fall, 80% of birds roost and feed on islands within 15 miles of each other.
Each fall, piled up on islands near Cape Avinof, the barges gorge themselves until they double their body weight. In August and September, fist-sized birds leap through the air in front of storm systems, helping them escape Alaska.
Once in the sky, some birds don’t stop flying for a week or more, losing half their body weight and possibly even dozing on the wing on a non-stop flight to New Zealand and Australia. The trip is over 7,000 miles long, the equivalent of a flight from San Francisco to New York, then back to San Francisco.
Scientists from Alaska and New Zealand have been monitoring barges for years using small satellite transmitters. In 2007, Bob Gill and others at the USGS Alaska Science Center in Anchorage noticed that a bird that took off from Alaska did not stop moving until it reached North Cape, in New Zealand.
In the spring, the return of the barges to Alaska is just as impressive. The birds take off from New Zealand and Australia and often fly straight for 6,000 miles to the Yellow Sea off China and Korea. The birds stay there for a few weeks before departing for Alaska, another nonstop of around 4,500 miles.
But things have changed along this road. Over the past 50 years, people have turned more than half of the biologically rich mudflats in the Yellow Sea into something else. These new land covers include deep-water ports, factories and shrimp farms.
With this much of the habitat disappearing, godwits must look elsewhere to find the clams and tag-sized aquatic worms that make up the bulk of their diet during migration.
The number of barges has declined, inspiring scientists to find new ways to count them in Alaska to continue the studies Bob Gill and others have conducted for decades.
In 2018 and 2019, biologists including Daniel Ruthrauff of the USGS Alaska Science Center flew over the deltas of the Yukon-Kuskokwim River and along the north side of the Alaska Peninsula in a single-engine aircraft. They searched for bar-tailed barges that were about to leave Alaska. Scientists used a digital camera with a 400-millimeter lens to take high-resolution digital photos of every barge flock they saw.
In what they consider their most accurate survey, the researchers noticed five herds with more than 80,000 barges in total located along a 15-mile chain of sandbanks near the mouth of the Kuskokwim River. . The total number of birds they found was around 100,000.
âIt’s rare to have so many individuals of a single species in a small place like this,â said Ruthrauff.
Sandbanks are great places for birds to roost as they are up to 6 miles offshore.
âAnd they’re so low and without features that it’s hard for the hawks to squeeze through the barges,â said Ruthrauff.
This mudflat hotspot that is home to nearly all of the world’s population of this remarkable creature in the fall (in summer, birds raise chicks on Alaska’s abundant insect population, tending to nests tundra as far as the northern slope) is vulnerable because it is so small.
âSome of the shoals are officially part of the Alaska Maritime National Wildlife Refuge,â said Ruthrauff, âBut the unnamed shoals where we detected most barges in 2019 have no official protection or designation. An untimely (oil) spill at the mouth of the Kuskokwim could literally wipe out the entire breeding population.
âIt’s a very important place.